1. Field of the Invention
The present invention relates to a microphone capable of being used in a place with a loud sound, and more particularly to a close-talking type microphone excellent in a noise shutting function.
2. Description of the Prior Art
The microphone receives various kinds of noises and sounds depending on use environments and a quality of receiving a target sound is frequently reduced or the target sound can not be frequently recognized. Accordingly, various countermeasures have been considered so as to reduce or prevent mixing of the noise and sound into the target sound.
The countermeasures mentioned above can be broadly classified into countermeasures by electric means and countermeasures by mechanical means. The countermeasures by the electric means is structured such as to remove an electric signal component on the basis of the noise and sound from an electric signal output by converting vibrations such as a sound pressure or the like by means of the microphone. In the countermeasures by the electric means, a process circuit there for is required and two microphones are commonly used as disclosed in Japanese Patent Laid-Open Gazette Nos. 57-119594 and 5-191884. Accordingly, the structure is effective with respect to a microphone fixed and placed to a specific place but can not be applied to a microphone used by being moved to unspecified places, particularly, a close-talking type microphone.
The countermeasures by the mechanical means includes a structure having a main object of removing a so-called wind noise such as a flight noise, a pop noise and the like by placing an open cell foamed body between a vibrating body and a cap disposed in a front surface thereof, as disclosed in Japanese Unexamined Patent Laid-Open Gazette Nos. 54-155820, 55-73195, 56-87998 and 8-322096. Further, as disclosed in Japanese Patent Laid-Open Gazette Nos. 56-27598 and 56-52993, there is a structure having a main object of preventing a so-called vibration sound generated by a mechanical vibration from outside by holding a microphone unit having a vibration body and an electric conversion portion in a case with employing an elastic material or a magnetic material in a floating state. Further, as disclosed in Japanese Patent Laid-Open Gazette No. 6-90491, there is a structure having a main object of shutting a loud sound by improving a close attaching property with respect to a close attaching type microphone such as a throat microphone, an ear-hole microphone, a bone conduction microphone or the like.
The structure in which the mechanical means is applied to the microphone itself as the sound countermeasure has an advantage that the microphone itself can be moved to an unspecified place and can be optionally used. However, in a place where a sound is too loud to normally talk or communicate over the telephone, in particular, a sound having a frequency and a sound pressure level equal to or more than those of a human voice is generated, such as a plant under operation, a construction field, a flying airplane, a running vehicle or the like, these loud sounds can not be shut by the structure mentioned above having the main object of preventing the wind noise and the vibration noise. Further, in the case of applying the structure of the close attaching type microphone to the close-talking type microphone to which the mouth is moved in close to talk, the structure has no effect against the loud sound.
An object of the present invention is to provide a close-talking type microphone which can shut a sound under a loud sound environment, does not make it hard or impossible for receivers to recognize a target sound due to a significant reduction of a quality of receiving the target sound, and does not accompany the problems mentioned above.
In order to achieve the problems mentioned above, in accordance with the present invention, there is provided a microphone comprising:
an outer casing having an open front surface;
an inner casing having a front wall provided with a sound hole in a center portion, the front wall closing the front surface, having a space on a peripheral surface and a rear surface, and inserted to the outer casing;
a sound pressure-electricity conversion unit fitted and held in the inner casing so as to direct a vibrating body toward the sound hole; and
a porous cap member covering the front surface of the front wall,
wherein the inner casing is made of a vibration isolating material, and the space is filled with a sound absorbing material constituted of a fiber laminated material.
The sound absorbing material charged in the space between the outer casing and the inner casing so as to surround the peripheral side surface and the rear surface of the sound pressure-electricity conversion unit has a significantly complex labyrinthine gap in comparison with the open cell foamed body, and irregularly disperses the sound pressure corresponding to a wave motion of the air so as to absorb. Further, the inner casing made of the vibration isolating material damps a vibration generated by the sound pressure passing through the sound absorbing material. Accordingly, it is possible to widely reduce or prevent the noise and the sound entering from the periphery through the outer casing from vibrating the vibrating body.
Further, the noise and the sound from the forward direction is shut by a speaker and does not reach the front surface of the microphone, so that the noise and the sound except the target sound hardly passes through the sound hole by speaking with positioning the mouth close to the cap member. Further, the front wall of the inner casing serves to damp the vibration generated by the noise and the sound going to enter from the front oblique direction, and in the case that the open cell foamed body is provided between the front wall and the sound pressure-electricity conversion unit or (and) the cap member, the shutting function of the noise and sound is more improved.
In this case, a natural or synthetic rubber is preferable for the vibration isolating material for forming the inner casing, and a glass wool is optimum for the fiber laminated material for forming the sound absorbing material.